DE3921217A1 - DRIVING DEVICE FOR THERMAL HEAD - Google Patents

Description

The present invention relates to a driver device or driver circuit for a thermal head and in particular a driver device for one Thermal head having a heat storage compensation circuit for High speed thermal recording with high quality is suitable.

The thermal head used for thermal recording includes a variety of heat-generating elements that are aligned with each other. Only the necessary ones heat generating elements are heated up in accordance with image data to produce a color on thermal recording paper, where Dye or ink or printing ink on a dye film on the recording paper is transferred for recording.

In a recording operation using such a thermal head, causes an increase in the recording speed or printing speed, that the printing of the next line is carried out before a sufficient one Diffusion and dissipation of heat energy, the heat generating elements has been supplied, has taken place, whereby thermal energy constantly or evenly is stored in the heat generating elements. It has been found that each heat generating element thermal energy according to its past heat generation stores what leads to variations in energy state, causing a deteriorated image quality is caused.  

When transferring dye from a dye film to the recording paper, would z. B. in a method of supplying the same thermal energy to each heat generating element without changing the history of heat generation the respective element is considered, to an accumulative addition the heat storage energy and the resulting total energy lead from what increased amount of transferred dye follows, causing smearing or This results in blurring of the printed characters or making it impossible for the desired field brightness or gradation through the tinting process by means of the density of each element.

In order to prevent a deterioration in the image quality, a heat storage compensation method is already in place proposed an appropriate one Amount of heat or amount of energy calculated for the respective heat-generating element from the current recording process of the respective heat-generating Elements and the record history of neighboring heat-generating Elements. However, this method requires that the record history each heat generating element is stored and required for accurate compensation with respect to a wide range of record data a correspondingly necessary large storage capacity.

Several attempts have been made to do this with a more precise method To develop heat storage compensation without a large storage capacity gets along, which is the disadvantage of the above method.

JP-A-60-161163 shows e.g. B. a heat storage compensation system for calculation the heat storage state of each heat generating element for the next recording operation from the current heat storage state every heat-generating element and an energy that just that is supplied, wherein the energy is compensated for the respective heat-generating Element is supplied, namely at the next printing or at the next opportunity based on the calculated storage states.

In this heat storage compensation system, the difference between one Target energy and the energy state of each heat-generating element in one Energy state memory (buffer) is stored as an energy used by the each heat-generating element is to be supplied. Furthermore compensated  a calculation circuit for the energy to be supplied the effect of a mutual Heat reaction between the respective heat generating element and neighboring ones or peripheral heat generating elements, whereby the optimal to be fed Energy or power is determined.

Furthermore, the value to be supplied to each heat generating element Indicates energy determined by the power supply calculation circuit Value added, which is the energy state of the respective heat-generating element after a single line print cycle that is provided by a heat diffusion calculation circuit is calculated. The result of the addition is stored in an energy state memory as an energy state of the respective heat generating element for printing or record the next line. The heat diffusion calculation circuit calculates the heat diffusion from the current one Energy states of each heat generating element and the neighboring or peripheral heat-generating elements and from the temperature of the thermal head substrate, which determines the energy status after a one-line printing cycle.

The calculation process in the heat diffusion calculation circuit of such known heat storage compensation system is so complicated that it is difficult is, the requirements of high print density and high sharpness or print quality or Adhere to resolution.

In the case of printing an original in B4 size at the printing rate of 400 DPI (dots / inch) and 2 msec per line is e.g. B. a total of 4096 heat-generating Elements needed and it is necessary to heat diffusion each pressure generating Elements within 500 msec.

This problem can be solved by a high speed device or a high speed technique such as B. Parallel processing or pipeline processing solved will. However, the increase in size and cost makes this device and the Device relatively impractical.

The present invention has been developed to solve the problems of those mentioned above to solve known devices or printers and it consists in a driver circuit for a thermal head to provide accurate heat storage compensation causes, with a simple circuit to thereby  high quality print image at low cost and even at high speed and generate high resolution.

In order to accomplish the above-mentioned task, typically the present invention, a thermal head driver device for determining and controlling of the energy created by each of the multitude of heat generating elements of the Thermal head is supplied in accordance with the print data, the Circuit or device a buffer memory for storing the pressure data supplied to it, a temperature detection device for detecting the Substrate temperature of the thermal head, a heat storage for storage the data of the heat storage state of a variety of heat generating Elements for each one-line printing cycle, a power supply compensation circuit for determining a pressure energy and a compensation energy that each heat generating Element is fed, based on the print data that is made up the buffer or buffer memory are output on the basis of the Temperature data output from the substrate temperature detection device and based on the heat storage data from the heat storage memory are output, further a heat storage calculation circuit for calculating heat storage data of each heat generating element for printing the next line based on the heat storage data each heat generating element from the heat storage memory are output and based on the pressure energy generated by the power supply calculation circuit is output, and further for feeding the calculated Heat storage data to the heat storage memory, thereby sequentially the heat storage data of the heat storage memory are updated, and an energy control circuit for controlling the energy that each heat generating Element of the thermal head is supplied, in accordance with the pressure energy and the compensation energy by the calculation circuit for the energy to be supplied.

According to one aspect of the present invention, the above-mentioned object of present invention fulfilled by the respective heat-generating element Compensation energy that is in accordance with the temperature variations of the Substrate of the thermal head is determined, and the print data (prehistoric Pressure data) is supplied from peripheral heat generating elements in addition to the energy required for printing for the heat generating element  under a hypothetical condition that the peripheral heat generating elements of the current heat generating element have been excited.

The compensation energy is based on the pressure data of the peripheral heat generating Elements and the substrate temperature of the thermal head in such a way determines that a constant heat storage of the pressure energy regardless of the Variations in the factors mentioned above are observed. As a result, the Heat storage calculation can be performed accurately, and only with the pressure energy and the heat storage amount of each heat generating element, whereby a complicated and expensive heat storage calculation is not necessary.

Further advantages, features and possible uses of the present invention result from the following description of exemplary embodiments in connection with the drawings. It shows

Fig. 1 is a block diagram showing the driving circuit for the thermal head according to an embodiment of the present invention;

Fig. 2 is a diagram for explaining an arrangement for printing image elements;

Fig. 3 is a block diagram showing an example of a configuration of a calculation circuit for the power to be supplied;

Fig. 4 is a block diagram showing another embodiment of the configuration for the power supply calculation circuit;

Fig. 5 is a block diagram showing an example of a circuit for resistance compensation;

Fig. 6 is a block diagram showing an example of the configuration of a heat storage calculating circuit;

Fig. 7 is a block diagram showing another example of the configuration of a heat storage calculating circuit;

Fig. 8 is a circuit diagram showing an example of the configuration of a thermal head;

Fig. 9 is a timing chart showing the operation of the thermal head shown in Fig. 8;

FIG. 10 is a block diagram showing a configuration of a power control circuit;

FIG. 11 is a timing chart for energizing time control;

Fig. 12 is a diagram showing the effect of a combination of excitation pulses;

FIG. 13 is a diagram for explaining the combinations of excitation pulses;

Fig. 14 is a block diagram showing an embodiment with an excitation pattern data reordering circuit;

Fig. 15 is a block diagram showing another embodiment of the excitation pattern data reordering circuit;

Fig. 16 is a detailed circuit diagram showing still another embodiment of the excitation pattern data reordering circuit;

Fig. 17 is a timing chart showing the operation of the excitation pattern data reordering circuit shown in Fig. 16;

Fig. 18 is a block diagram showing data transfer to the thermal head;

FIG. 19 is a timing chart showing the operation of the data transmission shown in FIG. 16.

A block diagram of a thermal head driver circuit according to an embodiment of the present invention is shown in FIG. 1, and a diagram for explaining an arrangement of print image cells is given in FIG. 2.

Shown in Fig. 1 is a peripheral pattern buffer memory connected to a buffer memory 1 for storing digital print data V _d supplied thereto, an energy supply calculation circuit 2 , which will be described in detail later Thermistor 3 , which is connected to a temperature detection device for detecting the substrate temperature of the thermal head, a heat storage memory 4 for storing the state of the amount of heat storage of each heat generating element at a predetermined time in a one-line printing cycle, an energy control circuit 5 for controlling the electrical power that each heat generating element of the thermal head 6 in accordance with the pressure energy e _p and the compensation energy e _r is zuaddiert, which is calculated in the Energiezuführberechnungsschaltung 2, and a heat storage calculating circuit 7, which will be explained below.

As shown in Fig. 1, the print image data V _{d associated} with each heat generating element is serially supplied to the peripheral pattern buffer 1 for each line.

The power supply calculation circuit 2 is sequentially synchronized with the transfer of the print image data V _d, the print data V _{d of} the peripheral heat generating elements and the heat generating elements output from the peripheral pattern buffer 1 , and the substrate temperature T _{h of} the thermal head generated by that the thermistor ( 3 ) arranged on the substrate of the thermal head is measured, and the heat storage data E _s , which indicate the heat storage amount of the respective heat-generating element, which are stored in the heat storage memory 4 and which are read out for the heat-generating element which is to be calculated (the heat storage data for each one-line printing, as will be explained later, updated and saved). The energy supply calculation circuit 2 generates an optimal pressure energy E _p and a compensation energy E _r .

The pressure energy E _p and the compensation energy E _r, which are sequentially generated by the Energiezuführberechnungsschaltung 2 are supplied to the power control circuit 5 and converted into excitation pattern data D, which are combined with the excitation pulse P to the supplied energy E of each heat generating element of the thermal head 6 to Taxes.

Furthermore, the printing energy E _p and the heat storage data E _{s of} a corresponding heat generating element are sequentially supplied to the heat storage calculation circuit 7 in synchronism so that the heat storage data E _s ' of the specific heat generating element is calculated and output for printing the next line. These data are stored sequentially in the heat storage memory 4 and used for the calculation of the energy to be supplied at the time of printing the next line.

In this configuration, the optimal energy to be supplied is determined by the energy supply calculation circuit 2 on the basis of the heat storage data in the heat storage calculation circuit 7 for each heat generating element, and the value thus obtained is used to control the energy to be supplied E in the energy control circuit 5 . thereby achieving high image quality printing in any heat storage condition. A detailed explanation is given below.

The buffer memory for peripheral pattern 1 has a serial input / parallel output shift register with a plurality of bits for holding and generating a plurality of successive or continuous pixels (image units) of the print image data V _d which are supplied to them serially. The data held and output in the peripheral pattern buffer 1 corresponds to the print data V _{d of} the current heat generating element and its peripheral heat generating elements for which the supplied power needs to be determined, and the bit number of this data becomes out the number of peripheral heat-generating elements, of which a mutual reaction or influencing must be considered.

An arrangement of pixels is shown in FIG. 2. According to the present embodiment, the cross-hatched print data D ₀ of the respective heat generating element and the print data D _-1 and D ₁ of adjacent heat generating elements are regarded as having an influence on the energy supplied as explained below.

The power supply calculation circuit 2 is with the pressure data D _-1 , D ₀ and D ₁ from the buffer memory for peripheral patterns 1 , the substrate temperature T _{h of} the thermal head, which is detected by the thermistor 3 , arranged on the thermal head substrate, and the current heat storage data E. _{s of} a current heat-generating element, which is stored in the heat storage memory 4 . These data are read out and sequentially fed to the circuit 2 in synchronism with the transmission of the print image data V _d , whereby the optimal feed energy E is determined.

The supply energy E is divided into the printing energy E _p , which is used for printing (which changes depending on the printing conditions, as mentioned below), and the compensation energy for maintaining a constant relationship (with a fixed energy for printing pixel dots) between the printing energy E _p and the variation of the heat storage state, which are output sequentially.

In the following, the way in which the supply energy is determined in the Explained in detail.

The printing energy is always calculated on the assumption that the printing data D _-1 , D ₁ of adjacent heat-generating elements are the same, ie that the pressure energy is supplied to the adjacent heat-generating elements. The pressure energy E _p is thus determined by the calculation, as shown below, from the substrate temperature T _{h of} the thermal head and the heat storage data E _s .

If D ₀ is "0", E _p = 0, and
If D ₀ = "1", E _p = E ₀- E _s - E _t (T _h ) (1)

Where E ₀ is the target energy required to print a given dot size, provided that D _-1 = D ₁ = 1, and where E _t , which is a function of substrate temperature T _h , to compensate for the change is in the target energy generated by the change in the substrate temperature T _{h of} the thermal head.

In fact, the pressure data D _-1 and D ₁ of adjacent heat generating elements are always "1", so that the heat radiation or spread and the cooling amount of a certain heat generating element during an excitation period are increased for an increased energy required to a given one Get point. Also during the cooling period or cooling period, a difference in the amount of heat radiation or cooling develops.

The change in the heat radiation and the cooling amounts of a specific heat-generating element, which is caused by the change in the pressure data D _-1 , D ₁ from neighboring heat-generating elements, is compensated for by the compensation energy E _r , whereby the energy distribution of the pressure point or dot is constant is held.

The value of the compensation energy E _r is determined by the values of the pressure data D _-1 , D ₀ and D ₁ and the substrate temperature of the thermal head, in the manner shown in Table 1 below.

Table 1

As can be seen, the compensation energy E _{r is determined} separately for the excitation period and the cooling period.

In the table above, E ₁ and E ₃ denote the value or amount of energy that flows directly into a particular heat-generating element from neighboring heat-generating elements when D ₀ = "0" and D _-1 = "1" or when D ₁ = "1" is during the excitation period or cooling period.

E ₂ and E ₄ on the other hand denote the amount of energy that flows away from a certain heat-generating element into neighboring heat-generating elements when D ₀ = "1" and D _-1 = "0" or when D ₁ = "0 ". The amount of heat storage has only a small influence on these energy values, which depend essentially on the substrate temperature T _{h of} the thermal head, and therefore all these values are a function of T _h .

Accordingly, the pressure energy E _{p is determined} independently of the pressure data from adjacent heat-generating elements by supplying the compensation energy E _r . On the other hand, since the change in energy of the current heat generating element is dependent on the value E _{p of} the pressure energy, only the pressure energy E _{p is} used to calculate the heat storage data of the current heat generating element.

Fig. 3 is a block diagram showing an example of the configuration of the Energiezuführberechnungsschaltung, and Fig. 4 is a block diagram showing another example of the configuration of the Energiezuführberechnungsschaltung.

As shown in Fig. 3, the print data D ₀, D _-1 and D ₁ of a current heat generating element and the adjacent heat generating elements, the digital data T _h 'of the substrate temperature of the thermal head by converting the output T _{h of} the thermistor 3 are obtained from an A / D converter 8 , and the heat storage data E _s read out from the heat storage memory 4 are sequentially supplied as an address to an energy supply determination table (LUT) 9 or comparison table.

In accordance with the above method, the energy determining the Energiezuführbestimmungstabelle 9 has calculated in advance, the pressure energy E _p and the compensation energy E _r with respect to an input value, and is designed so that it sequentially generates values corresponding to the address input values or outputs.

Just as shown in FIG. 4, it is therefore possible to determine the pressure energy E _p and the compensation energy E _r by separate LUTs . In such a case, the print data D _-1 , D ₁ of adjacent heat-generating elements are not required for the address input of the print energy determination table LUT 10 , while no heat storage data E _{s are} required for the compensation energy determination LUT 11 , which saves the required storage capacity of the LUTs .

The energy that is supplied to each heat-generating element of the thermal head by changing the normal excitation time and / or the applied voltage controlled. According to the present embodiment, the supplied Energy, the heat storage data etc. as time data for explanation under the Condition treated that the energy control through the excitation time (energization time) is effected.

The resistance values of the heat generating elements of the thermal head are not uniform or the same, rather a difference develops in the thermal energy, which is generated for the same excitation time, namely with the increase in the Changes in the resistance value, and therefore compensation is necessary.

Fig. 5 is a block diagram showing an example of a resistance compensation circuit.

A compensation value Δ E based on a resistance value for each heat-generating element is stored in a resistance compensation value memory 12 . The compensation value E , which is only read out when the pressure data D ₀ is "1", for an output of the energy supply calculation circuit 2 , is added to the compensation energy E _r in an adder 13 and supplied to the energy control circuit 5 . The compensation value Δ E is a difference between the excitation time required for each heat generating element to generate a target energy and the excitation time required to generate the same target value with an average resistance value, and has a positive or negative value. In the same way, the output E _r 'of the adder 13 can have a negative value. Since the power control circuit which ultimately applied energy from the pressure energy E _p and the compensation energy E _r 'is determined 5 of FIG. 5, which contains the resistance value combination, the energy supplied but never takes a negative value.

In Fig. 1, the pressure energy E _p , which is generated by the energy supply calculation circuit 2 , together with the heat storage data E _{s of} a corresponding heat generating element of the heat storage calculation circuit 7 are sequentially supplied and the heat storage data E _s ' for the current heat generating element is calculated after a one-line printing cycle and sequentially supplied to the heat storage memory 4 . The heat storage memory 4 sequentially updates the stored data by means of the heat storage data E _s ', which are supplied to it sequentially. The heat storage calculation circuit 7 performs the calculation of the equation (2) below and determines z. B. The heat storage data that follows a single line print cycle.

E _s ′ = K ₁ E _s + K ₂ E _p (2)

Where K ₁ and K ₂ are factors that are determined by the one-line printing cycle. In other words, K ₁ is a reduction factor of heat storage energy E _s and K ₂ the ratio of the pressure energy E _p relative to the increase in the heat storage energy E _s.

A specific configuration of the heat storage calculation circuit 7 will be explained with reference to FIGS. 6 and 7.

FIG. 6 is a block diagram showing an example of the configuration of the heat storage calculation circuit, and FIG. 7 is a block diagram showing another example of the configuration of the heat storage calculation circuit.

As shown in Fig. 6, the heat storage data E _s and the pressure energy E _p , which are sequentially supplied to the circuit, are multiplied by K ₁ and K ₂ in multipliers 14 and 15, respectively, and added in an adder 16 and finally in one FIFO memory (first-in / first-out) 17 written .

The FIFO memory 17 is used for storing the heat storage data E _s, since the heat storage data E _s to be read out sequentially at high speed, and is written and wherein the read and write operations are as desired independently of one another.

The FIFO memory 17 can be replaced by the switching operation of two line buffers 18 and 19 as shown in FIG . Also, as shown in Fig. 6, the heat storage calculation performed by the multipliers 14 and 15 and the adder 16 can be replaced by the calculation using the heat storage calculation table LUT 20 in which the result of the heat storage calculation is stored.

In Fig. 1, the energy control circuit 5 determines and controls the energy supplied to each heat generating element based on the pressure energy E _p determined in the energy supply calculation circuit 2 and the compensation energy E _r . As described above, according to the present embodiment, the energy is controlled by changing the excitation time.

With the increase in printing speed it becomes necessary to be accurate and fine Energy control within a short period of time or a short period of time to execute. The energy control, which is explained below, is for both Periods used, however, only the energy control during the excitation period explained.

FIG. 8 shows an example of a circuit configuration of the thermal head 6, and FIG. 9 shows a timing diagram for the data transmission. The thermal head 6 includes a heat generating section 100 and a heat generation driver 200 . The heat generating section 100 corresponds to a collection of heat generating elements 31 . This example shows a case with 4096 units of heat generating elements 31 . The excitation driver 200 is internally divided into a plurality of blocks for increasing the data transmission speed, each block being designed to be provided with data. In the case shown in Fig. 8, the excitation driver 200 is divided into 16 units of blocks 1-16 and has data input lines DIN 1-DIN 16 for the respective blocks. Excitation data R (0) for the heat generating element No. 0 to excitation data R (255) for the heat generating element No. 255 are supplied via DIN 1. Similarly, R (256) to R (511) are supplied with DIN 2 and R (3840) to R (4095) with DIN 16. Since each block has the same operation, only one of them is explained below.

Each block of excitation driver 200 includes 256 amplifiers 32 , 256 AND gates 33 , a 256-bit latch register 34 and a 256-bit shift register 35 , thereby independently controlling the control of the excitation of the 256 heat generating elements. The excitation data, which are supplied sequentially via the data input connections, are stored sequentially in the shift registers 35 in synchronism with the data transmission clock on the clock lines or connections. As soon as the shift registers 35 are filled, all data in the shift registers are latched into the latch register 34 at the same time, in synchronism with the latch pulse or latch pulse applied to the latch line. The excitation data thus latched in latch 34 is supplied to an AND gate 33 along with an excitation pulse on the selection line (strobe) and the resulting output is used to drive amplifier 32 which is connected to each heat generating element 31 , whereby the excitation control of the heat generating element 31 is carried out. In short, the excitation pulse supplied to the strobe wire and the excitation data latched in the latch register 34 are supplied to the heat generating element 31 for a "1" period at the same time for heat generation.

Fig. 10 is a block diagram showing an example of the configuration of the power control circuit 5.

The line buffer 300 contains two sets of RAM 24 (random access memory) that are switched for each line, and the energy E to be supplied is stored for one line and generated during the next line printing cycle. The energy to be supplied E , which is generated or output from the line buffer memory 300 , is converted into excitation pattern data D by means of an excitation pattern conversion table LUT 21 and further rearranged or rearranged in order to be suitable for transmission to the thermal head 6 by means of the excitation pattern data reordering circuit 29 . The resulting data is stored in the line buffer 400 . Line buffer 400 stores a single line of excitation pattern data D thus rearranged by switching the two RAM sets 27 , and at the same time generates excitation pattern data stored in the previous line cycle. This excitation data D and the generation of pulse P that is generated in the exciting pulse generating circuit are supplied to the thermal head 6, to control the energization time duration for each heat generating element of the thermal head. 6

An excitation period for a given heat generating element to produce a single pressure point is divided into a plurality of sections, each section being weighted differently. For each section so weighted, "0" or "1" data is transferred to the thermal head 6 to the excitation control section of the heat generating element so that the excitation is inhibited for the section in which "0" is transmitted while the excitation is effected during the weighting period in which "1" is transmitted, thereby performing excitation control of each heat generating element. In this way, the excitation section is selected for each heat generating element and the sections so selected are combined to control the excitation time. According to this embodiment, each section is assigned to a selection signal of the thermal head 6 . The following explains the case in which an excitation period is divided into eight sections of equal length. Until the minimum interval of division is limited by the time required for unit data transfer to thermal head 6 , there is no limit to the number of divisions for which it is not necessary to be divided into equal intervals.

In the event that the excitation time is controlled with eight divisions, there is a maximum number of controllable values or levels if the respective sections are weighted, such as, 1, 1/2, 1/4,. . ., 1/64, 1/128. A timing diagram for data transfer and excitation pulses under such conditions is shown in FIG. 11.

The characters P 1 to P 8 in Fig. 11 (a) denote excitation pulses which have a relative time between 1/128 to 1 as a result of the weighting.

The reference numerals D 1 to D 8 denote data for printing a single predetermined printing dot or dot, and are identified with "0" or "1" to determine whether a particular heat generating element is energized during each equally divided section. Therefore, if D 1 is 1, the current element is excited by a pulse P 1 , and if D 1 is 0 it is not excited by the pulse P 1 . If D 1 = D 3 = D 5 = D 7 = 1 and at the same time D 2 = D 4 = D 6 = D 8 = 0, the current element is excited by the pulses P 1 , P 3 , P 5 and P 7 .

The thermal head contains a shift register and a latch register. The data D 1 to D 8 , which are sequentially supplied to the shift register for each heat-generating element, are also sequentially transferred to the latch register by means of the buffer pulses LP 1 to LP 8 individually.

In detail, when the data D 1 associated with each heat generating element is held in a register in the 1st stage, the entire data D 1 is simultaneously transferred to the shift register in the 2nd stage by means of the latch pulse LP 1 for excitation control of the heat generating element, and at the next time when the data D 2 associated with each heat generating element is held in the 1st stage shift register, the data D 2 as a whole becomes the 2nd stage shift register by means of the latch pulse Transfer LP 2 . A similar process is carried out for the subsequent stages of data.

The excitation of each heat-generating element is controlled by means of the data in the latch register and therefore when an excitation pulse P 1 by means of the data D 1 during the excitation z. B. is supplied, the next data D 2 can be supplied to the shift register at the same time.

With an excitation which generates an excitation pulse obtained by the above-mentioned weighting procedure, the maximum excitation time of a given heat generating element is obtained when all of the data D 1 to D 8 are "1", that is, 1/8 (1st + 1/2 + 1/4 + 1/8 +... + 1/128) = 1/4. The actual excitation time is therefore usually less than 25% of the specified excitation duration, with the result that the applied voltage would necessarily have to be increased if the effective length of the thermal head were reduced. An excitation pulse of extremely short duration, on the other hand, is undesirable because an unstable excitation effect would be generated. Therefore excitation pulses P 1 ' to P 8' with the following weights are assumed, for. E.g .: 2/32, 3/32, 4/32, 8/32, 16/32, 32/32, 32/32, 32/32.

Furthermore, in order to stabilize the influence of an excitation pulse of short duration, the magnitude of the excitation pulses P 1 to P 8 and their positions within divided sections are changed.

As shown in Fig. 12 (a), in the case where the excitation pulses P 1 , P 2 and P 3 are separated from each other, the effect of the short pulse P 1 becomes particularly small and unstable. However, when the excitation pulses are close to each other, as shown in Fig. 12 (b), the effect of the short duration pulse also becomes very stable. An example is shown in Fig. 11 (b). A short duration pulse is placed before and after a longer pulse, and all of the pulses are located adjacent to one another to produce a single continuous pulse, thereby maintaining the stabilizing effect of each excitation pulse.

In the case of weighting, the relative pulse width of the excitation pulses P 1 ' to P 8' is 1/8 (2/32 + 3/32 + 4/32 + 8/32 + 16/32 + 32/32 + 32/32 + 32/32) given, namely for the maximum excitation time of a given heat-generating element of more than 50% of a predetermined excitation period. The excitation time can be changed by a combination of the excitation pulses P 1 ' to P 8' , as shown in Fig. 13, and controllable in 128 steps from 0 to 129/32 (except for 1/32 and 128/32).

In controlling the excitation time according to the above-mentioned kind, it is necessary to convert the energy E supplied to each heat generating element into corresponding excitation pattern data D (a combination of data for divided terminals D 1 to D 8 for selecting excitation pulses corresponding to E) converted. This conversion is effected by means of an excitation pattern conversion table LUT , which stores excitation pattern data for the applied energy E , as shown in FIGS. 14 to 16.

The excitation pattern data conversion (reordering) circuits shown in FIGS . 14 and 15 are configured within the power control circuit shown in FIG. 1.

As mentioned above, the length of the minimum divided section is not less than the time required for the first data transfer to the thermal head 6, and therefore it is necessary to shorten the data transfer time if an accurate power control with many partitions Allocations should be created. One method of shortening the data transfer time is to divide the 1st stage shift register on the thermal head into a plurality of blocks and to provide each block with a data input line, thereby ensuring a simultaneous transfer of a plurality of data. If a shift register is divided into a number of n blocks with a number of n data input lines e.g. B. is divided, the data transfer time is reduced by a factor of n .

However, due to the fact that the applied energy E or power is sequentially transferred to the heat generating elements, the excitation pattern data D (D 1 to D 8 ) generated by the excitation pattern conversion LUT also become the heat generating elements in a sequential manner and way transferred. When data is transmitted to the addresses of the heat generating elements in parallel in blocks, it is necessary to rearrange the excitation pattern data D.

Fig. 14 shows an example of a Erregungsmusterdatenumordnungsschaltung.

An explanation will be given with reference to the case of Fig. 14, in which the thermal head 6 has 4096 heat generating elements which are aligned in line and divided into 16 blocks each having 256 elements.

It is assumed that the 4096 heat generating elements are numbered (addresses) from 0 to 4095. The applied energy E (i) which is sequentially supplied to each element is converted into excitation pattern data D (i) (i : 0 to 4095) by means of the excitation pattern data conversion table LUT 21 and are sequentially stored in blocks in 16 storage units 22-1 to 22-16 . The character D (0) z. B. the excitation pattern data of the heat generating element No. 0. During the printing cycle of the next line, the data stored in the storage units 22-1 to 22-16 are read out and transferred to the thermal head for printing. The memory units 22-1 to 22-16 thus consist of two line buffers which are switched for each line to carry out the read and write operations (while one of the line buffers is being used for writing, the other is being read). The excitation pattern data D (0 + j) , D (256 + j),. . ., D (3480 + j) (j : 1 to 255) are read sequentially from the storage units 22-1 to 22-16 . All pattern data read from each memory unit consist of 8 bits D 1 to D 8 . First, the data D 1 associated with the excitation pulse P 1 for the first division section is selected at the same time by the data selectors 23-1 to 23-16 for transmission to the thermal head, then the data D 2 is selected and to the thermal head transfer. Similarly, a bit of data corresponding to D 1 to D 8 is read out eight times from the storage units 22-1 to 22-16 . Likewise, the excitation pattern data D 1 to D 8 are selected simultaneously by the data selectors 23-1 to 23-16 and transmitted simultaneously to the thermal head. The above embodiment requires a plurality of storage units or the like and involves the problems of high cost and complex circuitry.

Fig. 15 shows an example of a reordering of excitation pattern data using a simple circuit with shift registers and random access memories (RAM).

In the case of Fig. 15, the power to be supplied E (i) representing one line is provisionally stored in a RAM 24 , a first random access memory with an address i (i : 0 to 4095) corresponding to the number of the heat generating elements, saved. The data is read and rearranged in the print cycle of the next line. The power E (i) to be supplied (ie, the associated signal) read out from the RAM 24 is converted into excitation pattern data D (i) in the excitation pattern conversion table LUT 21 so that the bit data from D 1 (i) to D 8 (i) corresponding to the excitation pulses of each divided section are supplied to the shift registers 25-1 to 25-8, respectively. D 1 (i) to D 8 (i) represent the excitation pattern data D 1 to D 8 assigned in the i- th heat generating element.

The outputs of the shift registers 25-1 to 25-8 , which are of the serial input / parallel output type, are latched in the latch memories 26-1 to 26-8 whenever eight data are stored and sequentially in the RAM 27-1 or 27-2 , which is assigned to the second random access memory.

The data transfer to the thermal head and the printing are effected in the printing cycle of the next line. As a result, the RAM 24 and the RAMs 27-1 and 27-2 that reproduce two lines are each switched to perform a read and write operation separately for each line.

Fig. 16 shows a detailed configuration and Fig. 17 is a timing chart referred to to describe the operation in more detail.

The supplied energy E (i) read out from the RAM 24 for the i- th heat generating element is shaped in a latch 28 and is converted into excitation pattern data Dk (i) (k : 1 to 8) by means of the excitation pattern conversion table LUT 21 converted in appropriate time. The data Dk (i) thus converted, which are given in a combination of bit data D 1 to D 8 and are respectively associated with the excitation pulses P 1 to P 8 , as mentioned above, become the shift registers in parallel 25-1 to 25-8 fed each. The operating or processing processes are carried out in synchronism with a basic clock signal SCK ( FIG. 17). The address FRA for reading the data E (i) from the RAM 24 is changed in the following manner (E (i) in Fig. 17).

The following data Di (0) to Di (4095) are thus sequentially fed to the shift register 25-1 :

where D 1 (0) z. B. Excitation pattern data corresponding to the excitation pulse P 1 for the heat generating element No. 0. The shift registers 25-2 to 25-8 are also supplied with the data D 2 (i) to D 8 (i) in a similar sequence in a parallel manner to the data D 1 (i) (Dk (i), k = 1 to 8 in Fig. 17). The output signals of the shift registers 25-1 to 25-8 are simultaneously buffer- stored in the latch memories 26-1 to 26-8 by means of the clock LCK , specifically eight data (such as i = 0, 256, 512,... ., 1792).

The latches 26-1 to 26-8 , which are provided with the (output control), are provided to generate the buffered data only during the period when "0" remains. The data latched in the latches 26-1 to 26-8 are sequentially generated in accordance with the signals to and sequentially first supplied to the RAM 27-1 . If the latch 26-1 or D 1 (0), D 1 (256), D 1 (512) to D 1 (1792) temporarily stores, then the latch 26-2 stores D 2 (0), D 2 (256 ), D 2 (512),. . ., D 2 (1792) between. Similarly, latch 26-3 stores D 3 (0), etc., and latch 26-8 stores data D 8 (0), D 8 (256),. . ., D 8 (1792). Furthermore, the data D 1 (0) to D 1 (1792) of the latch memory 26-1 are generated by and supplied to the RAM 27-1 . Next, the data D 2 (0) to D 2 (1792) of the latch 26-2 are generated by and supplied to the RAM 27-1 . Similarly, the data of each latch is generated by through. In response to the switching of the chip select signal and the write turn-on signal , the RAM 27-1 and RAM 27-2 alternatively perform the write operation to store all the data half by half and thus the next eight data (e.g. B. i = 2048, 2304,..., 3840) compared to RAM 27-2 and read out. The chip selection signals and are intended to be switched alternatively. As a result, the data shown in Table 2 are sequentially read out from the latches 26-1 to 26-8 for the RAM 27-1 .

Table 2

Similarly, the data in the table below is sequentially read out from the latches 26-1 through 26-8 for the RAM 27-2 .

Table 3

On the other hand, the addresses SWA of the RAMs 27-1 and 27-2 in which this data is written are changed in the following manner.

In relation to this, the data D 1 (0) to D 1 (1792) are written by means of the signal at the address 0 of the RAM 27-1 , the data D 2 (0) to D 2 (1792) which by means of the signal in the Addresses 256 of the RAM 27-1 are generated, etc., until the data D 8 (0) to D 8 (1792) generated by the signal have been written into the address 1792 of the RAM 27-1 and subsequently in similar way. In the process, RAM 27-1 and RAM 27-2 store data completely rearranged, as shown in Tables 4 and 5 below.

Table 4

Table 5

After that, as shown in Fig. 18, the data stored in the RAM 27-1 and RAM 27-2 is simply read out simultaneously from bits 1 to 8 (I / O 1 to I / O 4) of each RAM, respectively and transferred in parallel to each heat generating element of each block of the thermal head in accordance with the order of the addresses i . An associated timing diagram is shown in FIG. 19. More specifically, the 256 heat generating elements of the first block are sequentially loaded with D 1 (0) to D 1 (255), the 256 heat generating elements of the second block are supplied in parallel with D 1 (256) to D 1 (511) in a sequential manner and in a similar manner, the same happens for subsequent blocks until the 16th block is loaded with data D 1 (3840) through D 1 (4095). After completing the supply of the signal D 1 to the 4096 heat generating elements for one line in this manner, the signals D 2 to D 8 are sequentially supplied like each heat generating element of each block in a similar operation.

Instead of changing the read address FRA of the RAM 24 and the write address SWA of the RAM 27-1 and RAMs 27-2 in the above case of rearrangement, it is also possible to change the write address PWA of the RAM 24 or the read address SRA of the RAM 27-1 and RAMs 27-2 to use.

Furthermore, although the thermal head 4096 has heat generating elements and in 16 Blocks according to the embodiment described above is the invention just as easily applicable to a thermal head that is different different Has numbers of heat-generating elements and in different numbers is divided by blocks in which the number of buffers or latches or the order of the addresses is changed.

Furthermore, instead of weighting the divided sections of the arousal period by changing the excitation time as in the embodiment above, can perform the same function with the same effect by changing the applied voltage for the divided sections or by a combination of those described above Method and a change in the applied voltage can be achieved.

According to the present invention, fine, precise energy control is included high resolution using a simple circuit and heat storage calculation facilitated.  

It is therefore easy to understand from the previous description that accordingly of the present invention, a driver circuit for a thermal head is given, by means of which a precise heat storage compensation effect is obtained with a simple circuit, a high quality print image is obtained low cost generated even when high speed operation and a printing operation high resolution.

Claims (7)

1. A thermal head driver device comprising:
a thermal head ( 6 ) having a plurality of heat generating elements;
a buffer memory ( 1 ) for storing record data which are fed to it,
temperature detection means ( 3 ) for detecting the temperature of the substrate of the thermal head;
a heat storage memory ( 4 ) for storing by updating the heat storage data E _s reflecting the amount of heat stored in each of the heat generating elements for each one-line recording cycle;
a power supply calculation circuit ( 2 ) for calculating the power supplied to each heat generating element based on the record data output from this buffer memory, the temperature data output from the thermal head substrate temperature detection device, and the heat storage data supplied are output from the heat storage memory;
a heat storage calculation circuit ( 7 ) for calculating the heat storage data for the recording of the next line based on the heat storage data of each heat generating element output from the heat storage memory to sequentially refresh the heat storage data stored in the heat storage memory by the result of the calculation which is supplied to the heat storage memory; and
an energy control circuit ( 5 ) for controlling the electric power supplied to each heat generating element of the thermal head in accordance with the energy calculated by the energy supply calculation circuit, the energy supply calculation circuit comprising means for calculating the recording energy E _p for each heat generating element based on the record data which are output from the buffer memory, the temperature data T _h which are generated by the temperature detection device of the thermal head substrate, and the heat storage data E _s which are produced by the heat storage memory and the device for calculating the compensation energy E _r on the basis of the recording data E _p and Temperature data are generated. 2. Driver device for a thermal head according to claim 1, characterized in that the heat storage calculation circuit calculates the heat storage data E _s ' for recording the next line by means of the function of the recording energy E _p , which is generated by the energy supply calculation circuit. 3. Driver device for thermal head according to claim 1, characterized in that that the energy control circuit controls the energy that each heat generating Element is supplied in such a way that each excitation cycle into one Variety of periods is divided, with the excitation energy for each of the divided periods is differentiated and the combination of actually excited periods are changed from all of the divided arousal periods becomes in accordance with the output of the power supply calculation circuit. 4. Driver device for a thermal head according to claim 1, characterized in that the energy control circuit comprises:
a first random access memory ( 24 ) for temporarily storing a line of data that is continuously transmitted,
a plurality of serial input / parallel output shift registers ( 25-1 to 25-8 ) which are sequentially supplied with data generated from the first free access memory,
a second random access memory ( 27-1 , 27-2 ) for sequential storage of output signals of the shift registers and
a data conversion circuit ( 21 ) for operating the read and write addresses of the first and second random access memories to rearrange the continuously transmitted data into a form suitable for transmission to the thermal head which is divided into a plurality of blocks and one Has data input line for each block. 5. A thermal head driving device for controllably supplying power to each of the plurality of heat generating elements of the thermal head in accordance with input record data, the device comprising:
means for dividing each excitation cycle into a plurality of periods;
means for determining different quantities of excitation for the divided periods; and
means for selectively combining actually excited periods from the divided periods in accordance with the energy to be supplied. 6. A thermal head driver device for controllably supplying energy to each of the plurality of heat generating elements arranged in line on a thermal head in accordance with an input recording energy, the device comprising:
a first random access memory ( 24 ) for storing a line of continuously transmitted input data;
a plurality of serial input / parallel output shift registers ( 25-1 to 25-8 ) which are sequentially supplied with data output from the first random access memory;
a second random access memory for sequentially storing data output from the shift register;
data input means for dividing the elements into many blocks to connect the input means to each; and
a power controller ( 5 ) for addressing the first and second random access memories to read and write data therefrom, optimally rearranging the continuously transferred data and feeding the rearranged data to the input device. 7. A thermal head driver device for controllably supplying power to each of the plurality of heat generating elements constituting a thermal head in accordance with input record data, the device comprising:
a buffer memory ( 1 ) for storing the input record data;
temperature detection means ( 3 ) for detecting the substrate temperature of the thermal head;
a heat storage memory ( 4 ) for storing by updating heat storage data representing the heat storage amount of each heat generating element for each recording cycle;
a power supply calculation circuit ( 2 ) for calculating a recording energy E _p and a compensation energy E _r on the basis of the recording data output from the buffer memory, the temperature data output from the temperature detection means, and the heat storage data output from the heat storage memory the hypothetical condition that a heat generating element and adjacent heat generating elements are both excited under the given control, and the power supply calculation circuit compensates for the energy E _r by selecting a predetermined function of the substrate temperature of the thermal head in accordance with the excitation / non-excitation of the heat generating element and the neighboring ones heat generating elements are calculated to compensate for an energy cut at the time of the non-excitation of the adjacent heat generating elements;
a heat storage calculation circuit ( 7 ) for calculating heat storage data E _s ' for the next recording cycle from the heat storage data E _{s of} each heat generating element from the heat storage memory and the recording energy E _p from the energy supply calculation circuit, the results of these calculations being sequentially supplied to the heat storage memory to sequentially supply the heat storage memory Update heat storage data stored in the heat storage memory; and
an energy control circuit ( 5 ) for controllably supplying each of the heat generating elements in accordance with the recording energy and the compensation energy calculated by the energy supply calculation circuit.